Sophisticated flight control systems are required to handle the complex requirements of modern aircraft flight. As the number of aircraft and the percent utilization of aircraft, specifically takeoffs and landings, increases, air traffic control (ATC) becomes more complicated. Heightened sensitivity and awareness of the importance of preventing mid-air collisions and other accidents increases with the increase in air traffic. Air traffic increases have resulted in more numerous flight paths and less aircraft spacing. The demands put on aircraft navigation systems have correspondingly increased.
Typically, transport aircraft use conventional aerodynamic flight control (AFC) methods that involve maneuvering the aircraft by means of the aircraft control surfaces. These control surfaces, such as the ailerons, elevators, and rudders, manipulate airflow to allow for modification of the aircraft flight path. Maneuverability of an AFC based aircraft with a fixed thrust direction is controlled, to a lesser degree, by changing engine thrust magnitudes. An increased research effort is being placed on modifying the direction of the engine thrust by nozzle redirection capabilities or external adjustable vanes. Controlling thrust direction is known as thrust vectoring. See U.S. Pat. Nos. 5,782,431; 5,769,317; 5,687,907; 5,628,272, each of which is incorporated herein by reference.
Thrust vectoring allows for much greater control of an aircraft and has been studied extensively for use in military applications. Inhospitable conditions demand flexibility in the ability of the military to make use of various runway lengths for aircraft. When the only runway available is very short, the need exists for an aircraft that is able to perform vertical or short takeoffs and landings. The McDonnell Douglas/British Aerospace AV-8B Harrier II is a military aircraft that is capable of such maneuvers. Aircraft with variable type thrust delivery systems are capable of vertical or short takeoffs and landings.
Commercial aircraft do not incorporate hardware for producing a vertical thrust component. In normal aircraft operating environments, with adequate runway lengths and the like, there has not been a need for thrust vectoring. The exception is the use of thrust deflectors that are deployable upon landing to assist in slowing of the aircraft after touchdown. However, the inventor's believe that there is an unfulfilled need to improve collision and meteorological hazard responsiveness in aircraft in general and in commercial aircraft in specific.
Aircraft are very safe modes of transportation but there is always the chance that an aircraft may be involved in a collision with another aircraft, lose altitude unexpectedly or impact an object fixed to the ground.
"Controlled Flight into Terrain" is a term used to describe a situation where an aircraft, under control of the crew, is flown into terrain, an obstacle or water, with no prior awareness on the part of the crew of the impending collision. Avoidance of this type of mishap is addressed in this invention.
Another mishap this invention seeks to avoid is the loss of control of the aircraft due to weather and atmospheric phenomenon. Aircraft experiencing turbulence, in particular wind shear, are at risk to sudden changes in altitude. These sudden changes in altitude are, at the minimum, uncomfortable to passengers and crew and if radical will jeopardize the safety of the aircraft itself. This danger is more pronounced at takeoff and landing when the aircraft is at low altitude. The aircraft can lose altitude rapidly and possibly impact the ground due to the effects of wind shear.
Wind shear is a natural phenomenon that occurs primarily during thunderstorms. A large downburst of cold, dense air associated with a frontal system hits the surface of the earth and spreads horizontally undercutting the warmer air outside the zone of the cold air downburst. The mixing of the cold and warm air produces a rolling vortex and causes high velocity winds to surge in opposite directions. This phenomena is wind shear. The hazard presented by wind shear, according to the National Transportation Safety Board (NTSB), has, directly or indirectly, contributed to approximately fifty percent of all commercial airline fatalities between 1974 and 1985. The NTSB has determined that over six hundred lives have been lost since 1964 due to the effects of wind shear.
To help alleviate the problem caused by wind shear, all commercial carriers were required to install some form of wind shear detection/avoidance system on their aircraft by 1995. Various sensing hardware and techniques are available for an aircraft to determine if it is in a hazardous turbulence or wind shear condition. Methods and apparatuses designed for wind shear detection, such as Doppler radar, have been developed. Methods and apparatuses for position and attitude sensing, as well as wind shear detection, are necessary for the implementation of an aircraft stabilizing system. Various configurations of wind shear detection may be found in U.S. Pat. Nos. 5,050,087; 5,406,489; 5,648,782; 5,523,759; 5,093,662, each of which is incorporated by reference herein.
Collision avoidance is one consideration of flight control systems. Collision avoidance schemes are largely dependent on efforts of air traffic controllers tracking aircraft traffic. When a potential danger became evident or was detected, the air traffic controller would notify each of the aircraft involved and provide alternative flight paths. With the increase in volume of air traffic, the air traffic controller's responsibilities have increased as well. What was once an acceptable and manageable technique for managing the volume of aircraft has become less manageable. Aircraft intercommunications or ground based monitoring stations in conjunction with on board collision avoidance systems have provided for more effective collision avoidance infrastructure.
GPS based air traffic control and collision avoidance systems are disclosed in U.S. Pat. Nos. 5,740,047; 5,714,948; 5,638,282; 5,636,123; 5,610,815; 5,596,332; 5,450,329; 5,414,631; 5,325,302; 5,153,836; and 4,835,537, each of which is incorporated herein by reference.
Emergency control using thrust vectoring has been proposed for transport aircraft (U.S. Pat. No. 5,782,431). This patent only describes the apparatus and its operation and does not disclose any system for detection of the need for thrust vectoring. Specifically, it does not include any method of automatic control in the event of a dangerous situation that may require an immediate action faster than a manual response implemented by the flight crew. The system disclosed herein implements a fuzzy logic based control scheme to analyze the danger level and appropriately engage the thrust vectoring system, in conjunction with automatic flight control measures, for aircraft stabilization or collision avoidance.
Fuzzy logic is a well known and developed logic system which is a superset of Boolean logic. Since the world is primarily analog in nature, many situations cannot be analyzed in a simple binary analysis. Simply concluding that an event, element or condition is either "X" or is not "X" is seldom adequate in making a complex decision. For example, an aircraft's altitude cannot simply be distinguished by low or not low, high or not high. There are other factors that need to be factored into the equation. For instance, an aircraft that is flying at twelve thousand feet altitude is not necessarily "low" but in a mountainous region with peaks extending to twelve thousand feet "low" takes on a relevant new meaning. Fuzzy logic systems are designed to deal with these nuances and assist in decision output results dependent on a set of operating rules.
Bivalent Set Theory is limiting as a decision making system, when attempting to model problems involving "humanistic" issues, because membership in bivalent sets is mutually exclusive. To provide a level of utility beyond that resulting from Bivalent Set Theory the theory of Fuzzy Logic or Fuzzy Set Theory was developed. Fuzzy Set Theory provides for membership in more than one set thus allowing a transition band from one set to another. As an example, instead of saying the air speed of an aircraft went from medium to fast in a change of 1 knot/hour (400 knots=medium, 401 knots=fast), the fuzzy set theory permits the change to happen over 10, 20, or 30 knots. This represents a transition band where the speed has membership (of magnitude less than 1) in both the medium and fast sets.
If the current flight status (pilot commands, altitude, air speed, engine thrust magnitude, nozzle angle, etc.) and external weather conditions (wind speed, wind shear magnitude, etc.) of an aircraft are known, a fuzzy logic controller is able to make rapid decisions as to the magnitude of a hazardous situation. The fuzzy logic controller can also determine what corrective actions should be taken.
Providing fuzzy logic controllers with the ability to automatically engage both conventional aerodynamic flight control (CFC) and thrust vectoring flight control (TVFC), the fuzzy logic controller is able to make decisions as to what combination of the two flight control systems would best handle the hazardous situation.
Sophisticated systems for determining aircraft position exist and continue to be developed. Such systems are especially important to an emergency flight control system for controlling an aircraft in an emergency situation. One of the aeronautical navigation or geographic positioning technologies that exists for determining aircraft position is the global positioning system (GPS). In addition other navigation aid systems are available. For instance, the global orbiting navigation satellite system (GLONASS) is a system that is currently in use.
The core of GPS is a constellation of twenty-four (24) satellites which continuously transmit information that are used by GPS based navigation equipment for position determination. Using differential GPS (DGPS), very accurate position information is attained for navigation and other flight control functions. Various GPS based navigation techniques that are used in conjunction with this invention include U.S. Pat. Nos. 5,570,095; 5,548,293; 5,543,804, each of which is incorporated by reference herein. Since GPS systems provide very accurate and precise information as to the aircraft's location, then GPS systems are desirable systems that may be integrated into subsystems that can be used for flight control and/or emergency control of an aircraft.
There is an industry need for an improved flight control system for controlling an aircraft in emergency situations or for use in hands-off flight situations. The present invention discloses and provides a fuzzy logic based emergency flight control system with thrust vectoring and aerodynamic flight control capabilities, and the present invention overcomes the problems, disadvantages, and limitations of the prior art.